Endoscope systems have been in general use for many years for non-invasively viewing anatomical features such as tissues and organs inside the human body. Endoscope systems typically include an endoscope tip having a flexible or rigid insertion tube having a headpiece mounted at its proximal end and a viewing window at its distal end. The headpiece of an endoscope tip having a flexible insertion tube normally includes controls, such as wheels or levers, connected to the distal end of the insertion tube by control wires to steer the end of the insertion tube in different directions. By manipulating the controls, an endoscopist can direct the viewing window at the distal end of the insertion tube over a wide range of directions to view tissues and organs located adjacent the distal end of the endoscope tip. The insertion tube also normally includes an illumination device for directing light into the body in the vicinity of the distal end of the insertion tube. The illumination device is typically an optical fiber extending from a light source at the proximal end of the insertion tube to an illumination window at the distal end of the insertion tube. However, the illumination may also be a light source mounted at the distal end of the insertion tube and powered with electricity coupled through wires extending through the insertion tube. Endoscope tips also include a viewing device to allow the endoscopist to view anatomical features, such as tissues and organs, through the viewing window.
Endoscope systems may be used to simply view anatomical features, or they may be used to non-invasively conduct various diagnostic or surgical procedures within the body. Endoscope tips used for this purpose often include a biopsy channel extending through the insertion tube from an access port at the proximal end of the insertion tube to an opening at the distal end of the insertion tube. Biopsy and surgical instruments attached to the distal end of catheters may be fed through the biopsy channel of the endoscope tip and out the biopsy channel opening to position the instruments adjacent the viewing window of the endoscope tip. A biopsy or surgical procedure can then be performed by such techniques as manipulating the endoscope tip controls, advancing or retracting the endoscope tip within the body, advancing or retracting the catheter within the biopsy channel, or manipulating an actuator that is mechanically coupled to the biopsy or surgical instrument. Endoscope tips that do not have biopsy channels can also be used to perform biopsy or surgical procedures. In such cases, one or more biopsy or surgical instruments are introduced into the body by suitable means, such as by using a laparoscopic catheter. The biopsy or surgical instruments are then positioned within the field of view of the endoscope tip viewing window.
To improve performance, specialized endoscope tips have been developed to best accomplish their intended function. For example, upper endoscope tips are used for examination of the esophagus, stomach and duodenum, colonoscopes are used for examining the colon, angioscopes are used for examining blood vessels, bronchoscopes are used for examining the bronchi, laparoscopes are used for examining the peritoneal cavity, and arthroscopes are used for examining joint spaces. Instruments to examine the rectum and sigmoid colon, known as flexible sigmoidoscopes, have also been developed. The discussion of endoscope tips herein generally applies to these and other types of endoscope tips, and the term “endoscope tip” as used herein is meant to encompass all these and other such devices.
As mentioned above, endoscope tips include some form of viewing device for allowing anatomical features to be viewed through viewing windows. One type of viewing device uses a fiber-optic bundle extending from the viewing window at the distal end of the insertion tube to a viewing window on the headpiece. The fiber-optic bundle optically couples images throughout the length of the insertion tube. Another type of viewing device uses a miniature video camera positioned behind the viewing window at the distal end of the insertion tube. Wires extending from the video camera through the insertion tube couple power to the camera and video signals from the camera. Still another type of viewing devices uses a beam scanning device positioned behind the viewing window. Such scanned beam endoscope tips are a fairly recent innovation.
Regardless of which type of viewing device is used by an endoscope system, the image obtained by using the endoscope system may not accurately show the size, shape, color or other property of the anatomical features being viewed with the endoscope system. For example, it may be difficult to accurately asses the size of an internal object, such as a tumor, using any of the above-mentioned endoscope types. It may also be difficult to accurately show the true color of tissues or organs. For endoscope tips using optical fibers to view an image, the brightness of the image may be affected by light attenuation in the optical fiber. The color of the image obtained using an endoscope system may be affected, for example, by the spectral properties of the illuminating light or the spectral transfer properties of the optical fiber or video camera. Endoscope tips using cameras and beam scanners suffer from additional problems not encountered in endoscope tips using an fiber-optic bundle, such as the true contrast or sharpness of an endoscopically obtained image. And even endoscope tips using a fiber-optic bundle will suffer from these limitations if images obtained using the endoscope system are converted to digital form.
There is therefore a need for an image calibration apparatus and method that allows an endoscope system to be calibrated so that it can accurately portray anatomical features.